PRMT5, also described as Hsl7, Jbp1, Skb1, Capsuleen or Dart5, is one of the major methyltransferases responsible for mono- and symmetric dimethylation of arginines. Post-translational arginine methylation on histones and non-histone proteins seems to be crucial for a variety of biological processes, like genome organisation, transcription, differentiation, spliceosome function, signal transduction and regulation of cell-cycle progression, stem cells and T-cell fate [Stopa, N. et al., Cell Mol Life Sci, 2015, 72(11): p. 2041-59] [Geoghegan, V. et al., Nat Commun, 2015, 6: p. 6758]. Metazoan PRMT5 forms a functional complex with the methylosome protein 50 (MEP50) also named as Wdr77, androgen receptor coactivator p44 and Valois. Both, elevated PRMT5-MEP50 protein level and cytoplasmic accumulation are implicated in cancer tumorigenesis and have recently been correlated with poor clinical outcome [Shilo, K. et al., Diagn Pathol, 2013, 8: p. 201]. Cellular rescue experiments that addressed both the catalytic and scaffold function of the PRMT5-MEP50 complex, beside comprehensive enzymological studies have substantiate the oncogenic link between protein level, localisation and enzymatic function [Gu, Z. et al., Biochem J, 2012, 446(2): p. 235-41] [Di Lorenzo, A. et. al., FEBS Lett, 2011, 585(13): p. 2024-31] [Chan-Penebre, E. et al., Nat Chem Biol, 2015, 11(6): p. 432-7]. This correlation turns PRMT5 into an essential small molecule drug target against cancer and other diseases [Stopa, N. et al., Cell Mol Life Sci, 2015, 72(11): p. 2041-59].
PRMT5 is a member of the type II PRMT subfamily that utilises S-adenosylmethionine (SAM) to generate symmetric dimethylated arginine on histones and non-histone protein substrates and S-adenosylhomocysteine (SAH). The crystal structure of the human hetereo-octameric complex (PRMT5)4(MEP50)4 co-crystalised with SAH and a histone H4 peptide substrate illustrated the mechanism of methylation and substrate recognition [Antonysamy, S. et al., Proc Natl Acad Sci USA, 2012, 109(44): p. 17960-5]. The regulation of PRMT5 activity occurs through a vast number of different binding partners, post-translational modification cross talk, miRNAs and subcellular localisation.
Methylation of histones H2A and H4 on Arg3 and histone H3 on Arg8 regulate chromatin organisation for specific repression of gene transcripts that are involved in differentiation, transformation, cell-cycle progression and tumour suppression [Karkhanis, V. et al., Trends Biochem Sci, 2011, 36(12): p. 633-41]. Furthermore, PRMT5-mediated methylation of histone H4 on Arg3 might recruit the DNA-methyltransferase DNMT3A to couple histone and DNA methylation for long-term gene silencing [Zhao, Q. et al., Nat Struct Mol Biol, 2009, 16(3): p. 304-11].
Non-histone methylation can occur either in the cytoplasm or nucleus dependent on the cellular localisation of PRMT5. The methylation of the Sm proteins D1 and D3, which are required for the assembly of the nuclear splicesome, takes place in the cytoplasm as part of the PRMT5 containing “methylosome” [Friesen, W. J. et al., Mol Cell Biol, 2001, 21(24): p. 8289-300]. Further evidence for PRMT5 involved in splicing has been provided by the conditional PRMT5 knockout in mouse neural stem cells. Cells that lack PRMT5 showed a selective retention of introns and skipping of exons with weak 5′ donor sites [Bezzi, M. et al., Genes Dev, 2013, 27(17): p. 1903-16].
In addition to a role in splicing, PRMT5 influences key pathways involved in cell fate and homeostasis by direct methylation of key signalling nodules like p53 [Jansson, M. et al., Nat Cell Biol, 2008, 10(12): p. 1431-9], EGFR [Hsu, J. M. et al., Nat Cell Biol, 2011, 13(2): p. 174-81], CRAF [Andreu-Perez, P. et al., Sci Signal, 2011, 4(190): p. ra58], PI3K/AKT [Wei, T. Y. et al., Cell Signal, 2014, 26(12): p. 2940-50], NFκB [Wei, H. et al., Proc Natl Acad Sci USA, 2013, 110(33): p. 13516-21].
Since PRMT5 is one of the major sym-Arg methyltransferases and involved in a multitude of cellular processes, an increased protein expression appears to be an important factor in its tumorigenicity. Interestingly, the translation of PRMT5 in mantle cell lymphoma (MCL) seems to be regulated by miRNAs. Although MCL cells show less mRNA and a slower transcription rate of PRMT5 than normal B lymphocytes, the PRMT5 level and the methylation of H3R8 and H4R3 are significantly increased [Pal, S. et al., EMBO J, 2007, 26(15): p. 3558-69]. Re-expression of miRNAs that binds the 3′UTR region of PRMT5 decreases PRMT5 protein level [Wang, L. et al., Mol Cell Biol, 2008, 28(20): p. 6262-77]. Strikingly, a prmt5 antisense RNA has been found within the human prmt5 gene that supports the hypothesis of a specific translational regulation rather than high mRNA expression level [Stopa, N. et al., Cell Mol Life Sci, 2015, 72(11): p. 2041-59].
Although PRMT5 is considered as a clinical relevant target, very few selective PRMT5 inhibitors have been published, yet. Very recently, a novel sub-nanomolar potent PRMT5 inhibitor (EPZ015666) with anti-tumour activity in multiple MCL xenograft models has been described to be the first chemical probe suitable for further validation of PRMT5's biology and role in cancer [Chan-Penebre, E. et al., Nat Chem Biol, 2015, 11(6): p. 432-7].
Further development of specific small molecule inhibitors of PRMT5 may lead to novel chemotherapeutic approaches for cancer.
WO2014100695A1 discloses compounds useful for inhibiting PRMT5 activity; Methods of using the compounds for treating PRMT5-mediated disorders are also described.
WO2014100730A1 discloses PRMT5 inhibitors containing a dihydro- or tetrahydroisoquinoline and uses thereof.
Devkota, K. et al., ACS Med Chem Lett, 2014, 5: p. 293-297, describes the synthesis of a series of analogues of the natural product sinefungin and the ability of these analogues to inhibit EHMT1 and EHMT2.
WO02003070739 discloses partial and full agonists of A1 adenosine receptors, their preparation, and their therapeutic use.
WO2012082436 discloses compounds and compositions as modulators of histone methyltransferases, and for treating diseases influenced by modulation of histone methyltransferase activity.
WO2014100719 discloses PRMT5 inhibitors and uses thereof.
WO03074083 discloses combination therapies that selectively kill methylthioadenosine phosphorylase deficient cells. Analogs of MTA are described herein as anti-toxicity agents.
Kung, P.-P. et al., Bioorg Med Chem Lett, 2005, 15: p. 2829-2833, describes the design, synthesis, and biological evaluation of novel human 5′-deoxy-5′-methylthioadenosine phosphorylase (MTAP) substrates.
WO2012075500 discloses 7-deazapurine modulators of histone methyltransferase.
WO2014035140 discloses compounds and compositions for modulating histone methyltransferase activity.
WO02015200680 describes PRMT5 inhibitors and uses thereof.
There is thus a strong need for novel PRMT5 inhibitors thereby opening new avenues for the treatment or prevention of cancer, such as e.g. mantle cell lymphoma. It is accordingly an object of the present invention to provide such compounds.
The compounds of the present invention are structurally different and may have improved properties such as for example improved potency, or improved pharmacokinetics (PK) and oral bioavailability, compared with compounds disclosed in the prior art.